The present invention is a one-step Grignard-type process for preparation of organosilanes. The process comprises contacting magnesium metal with a mixture comprising an organic halide and a halosilane in a co-solvent comprising about one to 15 moles of a dialkyl ether comprising less than seven carbon atoms, per mole of the organic halide; and about 0.05 to less than two moles of a liquid aromatic hydrocarbon solvent per mole of the dialkyl ether; at a temperature within a range of about 5.degree. C. to 200.degree. C. The present inventors have found that the presence of the co-solvent comprising the dialkyl ether and the liquid aromatic hydrocarbon at the described molar ratios provides for a product slurry that stirs and flows easily. These characteristics of the product slurry improve mass transfer and heat transfer during conduct of the process and allow for easier separation of the organosilane from the product slurry. Conduct of the present process in the co-solvent provides for improved ratios of the desired organosilane to by-products and improved recovery of product from the resultant slurry. Furthermore, the use of the co-solvent allows the process to be run as a continuous process. The process can be self initiating when run within the described mole ratios of liquid aromatic hydrocarbon solvent to dialkyl ether. The process is particularly useful for making allyl substituted organosilanes.
The reaction of organic halides with magnesium metal in the presence of oxygenated solvents such as dialkyl ethers to form reactive complexes typically referred to as Grignard reagents is well known. The production and reactions of Grignard reagents has been the subject of books and numerous review articles. Such reviews are provided, for example, in Coates et al., ORGANOMETALLIC COMPOUNDS, Vol. 1, p. 76-103, (1967), Methuen and Co. LTD, London, U.K.; and in Kirk and Othmer, ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, Vol. 10, 721-734 (1966), The Interscience Encyclopedia, Inc., NY, N.Y. The structure of the Grignard reagent has not been determined with certainty. However, it is generally believed that the Grignard reagent exists as a complex in solution and that solvent can play a critical role in such complex formation. The unpredictable effect of solvent on the formation and reactivity of Grignard reagents is discussed in the above cited review articles.
The preparation of organic compounds, such as 1,5-hexadiene, by a process using a Grignard reagent as an intermediate is known. For example, Turk et al., Organic Synthesis, Vol. 27, 7-8, 1947, teach a process for preparing 1,5-hexadiene by the reaction of allyl chloride in anhydrous ether with magnesium turnings. Turk et al. teach that this reaction results in the formation of a thick slurry which becomes unstirrable. This unstirrable slurry is then treated with a hydrochloric acid solution until the magnesium chloride by-product is in solution and the slurry becomes sufficiently fluid to be stirred.
Such processes as taught by Turk et al. are not generally acceptable as a commercial process. The formation of the non-stirrable slurry during conduct of the reaction can cause reduced mass transfer and heat transfer and therefore reduced yield. Furthermore, the nature of the slurry makes it necessary to treat the slurry in an additional step with a reagent to solubilize the slurry to allow isolation of the product. Typically, a major portion of the product is trapped within the non-stirrable slurry. In addition, the non-flowable nature of the slurry does not allow for the reaction to be run as a continuous process.
It is an objective of the present invention to provide a one-step process for preparing organosilanes using a Grignard type reagent as an intermediate, where the process avoids many of the above discussed problems with Grignard type processes by creating a reaction mixture slurry that is flowable and easily stirred. Thus, mass transfer and heat transfer can be improved in the reaction mixture providing for improved yield of organosilane. In addition, the formation of a slurry that is flowable can allow for the conduct of the process as a continuous process. No additional step is necessary to solubilize the slurry to make it flowable and allow for recovery of the organosilane.
The present inventors have found that when an organic halide is contacted with magnesium in the presence of a halosilane and a co-solvent comprising a dialkyl ether comprising less than seven carbon atoms and 0.05 to less than 2 moles of a liquid aromatic hydrocarbon solvent per mole of the dialkyl ether, the resulting slurry is flowable and easily stirred. Furthermore yields of the organosilane are improved due to, for example, improved ratios of the organosilane to by-products and the ability to recover the product from the slurry. The flowable nature of the resulting slurry allows the process to be run as a continuous process.
Richards et al., U.S. Pat. No. 3,080,324, teach that an oxygenated solvent and a liquid hydrocarbon can be used as a reaction medium in the preparation of a Grignard reagent. Richards et al. do not teach that their co-solvent system is useful in subsequent reactions of the Grignard reagent with halosilanes.
Fletcher et al., U.S. Pat. No. 3,801,558, teach that advantages can be realized when the reducing agent used in preparing a magnesium-reduced catalyst is an organomagnesium Grignard reagent prepared in a hydrocarbon solvent medium containing a controlled amount of a complexing agent for the Grignard reagent such as dialkyl ether. The reported advantage is that the Grignard reagent may be more soluble in hydrocarbon solvents at ambient temperature. Fletcher et al. report the use of the Grignard as a reducing agent for titanium trichloride in a process for making a catalyst useful in polymerizing alpha-olefins.
The reaction of Grignard reagents with halosilanes is well known and many such reactions are described in Kharash et al., Grignard Reactions of Nonmetallic Substances, Prentice-Hall, Inc., New York, 1954, p. 1306-1331.
Takamizawa et. al., U.S. Pat. No. 4,593,112, teach a tert-hydrocarbyl silyl compound can be synthesized by reacting a tert-hydrocarbylmagnesium halide as a Grignard reagent with a silane compound having at least one silicon-bonded hydrogen atom and at least one silicon-bonded halogen atom simultaneously in a molecule in a suitable organic solvent. Takamizawa et al. suggest that the solvent may be a mixture of an ether and an aromatic hydrocarbon solvent.